Electrical insulating composition



May 6, 1969 R, G. FLOWERS ml., 3,442,834

ELECTRICAL INSULATING COMPOSITION Filed June 1B. 1965 United States Patent O 3,442,834 ELECTRICAL INSULATING COMPOSITION Ralph G. Flowers and Charles A. Winter, Pittstield,

Mass., assignors to General Electric Company, a corporation of New York Filed June 18, 1965, Ser. No. 465,015 Int. Cl. C08g 37/30; H01b 3/36, 3/38 U.S. Cl. 260-19 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to electrical insulation and more particularly to an improved wire coating enamel of the phenolic modified polyvinyl acetal type.

Wire enamel of polyvinyl acetal phenol-aldehyde composition has been widely used in the past for insulating conductors in various types of electrical apparatus, especially electromagnetic devices such as transformers. It has been found, however, that the dielectric and physical properties of known wire enamels of the above type tend to lose their otherwise excellent dielectric strength and other electrical properties when subjected to elevated temperatures, andespecially under high electrical stress. This problem thus unduly limits the operating temperature at which the electrical apparatus could otherwise be efficiently operated and may result in reducing the useful life of the apparatus. Care must also be taken to avoid the occurrence of even temporary overload conditions which might unduly raise the temperature of the insulating system.

It is an object of the invention to provide a novel cornposition of matter, and particularly improved electrical insulating material, having excellent electrical and physical properties even at elevated temperatures.

It is another object of the invention to provide electrical insulating material of the above type adapted for use as wire coating enamel and applicable to conductors for various types of electrical apparatus, and particularly for wire coils employed in electromagnetic devices such as transformers and the like.

It is a particular object of the invention to provide an improved wire enamel composition which is compatible with various types of dielectric uids used in electrical apparatus in which the wire is incorporated, and which imparts improved life and operating characteristics to electrical coils incorporating the wire, especially under conditions of elevated operating or overload temperatures.

It is another object of the invention to provide an insulated conductor having an insulating coating characterized by the above-described improved electrical and physical properties.

Other objects and advantages will become apparent from the following description and the appended claims.

With the above the above objects in view, the present invention in one of its aspects relates to electrical insulating material comprising the heat cured product of a mixture of a phenol-aldehyde modified polyvinyl acetal resin and a metal-organic compound, as more particularly disclosed hereinafter. The described insulating material, in accordance with another aspect of the invention, is further addition to the aforementioned mixture of a melamine derivative compound, specifically hexamethoxymethylmelamine.

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The invention will be better understood from the following description taken in conjunction with the accompanying drawing, in which:

FIGURE l is a cross-sectional view of an electrical conductor having a wire enamel coating thereon having a composition in accordance with the invention; and

FIGURE 2 is a graph showing the improved properties of insulating compositions of the present invention in comparison to a prior art insulating material.

The polyvinyl acetal resins employed in practicing the invention are hydrolyzed, polymerized vinyl ester aldehyde condensation products, which may be produced from various aldehydes and various polyvinyl esters, as disclosed in a number of places inthe art, as for example in the patents to Patnode et al. 2,085,995 and Daszewski 2,730,466.

Aldehydes which may be used in making the polyvinyl acetal resins include, for example, formaldehyde, acetaldehyde, propionic aldehyde, butyric aldehyde, benzaldehyde, and the like. Likewise, the polyvinyl esters employed may include polyvinyl acetate, polyvinyl butyrate, and the like.

The phenolic modified polyvinyl acetal resin used in practicing the invention is also well known and the method of making such a resin is disclosed, for example, in the patent to Jackson et al. 2,307,588, the disclosure of which is incorporated herein by reference. As there disclosed, this phenolic modified resin may be made by heat-treating a mixture of a polyvinyl acetal resin and a compatible heat-hardenable phenol-formaldehyde resin.

In accordance with the present invention, the phenolic resin modied polyvinyl acetal resin is improved in its ability to withstand higher temperatures by adding thereto certain metal-organic compounds. Particular metal-organic compounds which have provided satisfactory results in practicing the invention are zinc urea, lead naphthenate, zinc naphthenate, zinc octoate, calcium naphthenate, manganese naphthenate, cobalt naphthenate, and iron naphthenate. When such compounds are admixed with the phenolic-modified polyvinyl acetal resin and the mixture is heat-treated, the resulting material has been found t0 substantially thermally upgrade electrical apparatus in which it is used in terms of improved dissipation factor (power factor), and life characteristics.

In the manufacture of electrical apparatus such as transformers, for example, insulatingmaterials which can withstand higher operating temperatures are particularly desirable in view of current trends to make the transformers more compact (which increases heat dissipation problems) and to apply higher electrical stresses thereon in operation. It is known that electrical insulating mate rials in general produce dielectric loss at elevated tempcratures and since the dissipation factor is a relative index of dielectric loss, it has frequently been used for evaluation of electrical insulation, and especially its electrical properties under high temperature. Experience has shown that wire enamel (as well as other insulation material) in electrical equipment is subject to thermal runaway conditions when the operating temperature of the equipment increases to certain levels. 'Such thermal 1unaway is characterized by la sharp rise in the measured dissipation factor of the insulating material when such temperature levels are reached. Further increase lin operating temperature or continued operation at the thermal runaway point usually results in failure of the insulation and the interruption of operation of the electrical apparatus.

In tests made for evaluating and compa-ring various types of electrical insulation, the temperature at which the dissipation factor of the material reaches 50% has been used as an indicator of incipient thermal runaway conditions for purposes of comparison, and this temperature is referred to here as the dissipation factor (DF) surge temperature. The phenolic-modiiied polyvinyl acetal resin mentioned above, which has been extensively used heretofore for lwire enamel coatings, is usually characterized by a DF surge temperature of about 18S-190 C., and in this respect is better than other known wire insulating compositions such as epoxy, acrylic and oleoresinous type enamels. It has been found, however, that the lwire enamel composition of the present invention, which includes the aforementioned metal-organic additives, has a DF surge temperature of well over 200 C., and as a result imparts marked improvement in the power factor and life characteristics of the electrical apparatus in which it is used when subjected to elevated operating or overload temperatures.

It has been further found in accordance with the invention that the addition of hexamethoxymethylmelamine to the described resin mixture provides even greater irnprovement in the electrical as well as physical properties of the final insulating material. Thus, an additional increase in the DF surge temperature of 5 to 10 C. and smoother, more adherent coatings are achieved by use of this additive in combination with the phenolic-modied polyvinyl acetal resin and the metal-organic compound. The hexamethoxymethylmelamine additive is commercially available under the name Cymel 300 and is a low melting point solid (M.P. about 55 C.). The use of this melamine derivative in the wire coating mixture described, in addition to providing the above advantages, facilitates the wire coating process by enabling the use of higher temperatures for drying the wire enamel and permits greater speeds of the wire in passing through the coating and drying apparatus. A number of other compounds related chemically to hexamethoxymethylmclamine were t-ricd in place of the latter in the enamel composition, but these did not improve the electrical or physical properties of the wire enamel. Such other unsatisfactory additives included urca, N,N diallyl melamine, hexamethylenetetramine and triethylenediamine.

In general, the amount of metal-organic compound employed in the mixture should be such as to provide a range of about .25 to about 2.5 percent by weight of the metal component based on the weight of the total solids of the resin mixture. The content of the melamine derivative compound, Wihen used, should be in the range of about 1 to about 10% Iby weight of the total solids of the resin mixture.

FIGURE 1 shows a cross section of an electrical conductor 1, such as copper wire, coated with a wire enamel 2 having a composition in accordance with the invention.

The following examples illustrate compositions in ac cordance with the invention which provide marked improvement when used as enamel wire coatings, it being understood that the invention is not intended to be limited to the particular materials, proportions or procedures described:

EXAMPLE I Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.6 Zinc '(as zinc octoate) 0.4 Hexamethoxymethylmelamine (Cymel 300) 3.0

In this as well as the other examples described, the polyvinyl acetal phenol-formaldehyde resin was used in the form of a cresylic acid solution, and the zinc octoate, where used, was in the form of a solution in petroleum spirits, of which the zinc constituted about 8% by Weight.

The above ingredients are mixed together at room temperature and then applied to wire in a wire coating apparatus. The thus-coated wire is heated at temperatures in the range of about Z50-500 C., usually about 300 C., for heat hardening the wire enamel. Typically, about 8 coats of the wire enamel are applied in this manner upon the wire to provide a total thickness of about 4 mils.

The wire enamel thus produced in accordance with Example I was characterized by a DF su-rge temperature of 225 C. and the enamel produced a smooth, flexible,

tightly-adherent, abrasion-resistant insulating film on the wire.

EXAMPLE II Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.1

Zinc (as zinc octoate) 0.5 Hexamethoxymethylmelamine 3.4 50% DF temperature-231 C.

EXAMPLE III Percent by Weight Polyvinyl acetal phenol-formaldehyde resin 95.0 Lead (as lead naphthenate) 1.6 Hexamethoxymethylmelamine 3.4

50% DF temperature225 C.

The lead naphthenate was used in the form of a solution in petroleum spirits of which the lead constituted about 24% by weight.

EXAMPLE IV Percent by weight Polyvinyl acetal phenol-formaldehyde resin 97.5 Zinc (as zinc urea) 0.5 Hexamethoxymethylmelamine 2.0

50% DF temperature-120 C.

The zinc urea additive was made by mixing 60 grams of zinc oxide and 127 grams of urea in 567 grams of cresylic acid and heating the mixture at 200 C. for two hours.

EXAM-PLE V Percent by weight Polyvinyl acetal phenol-formaldehyde resin 99.5 Zinc (as zinc urea) 0.5v 50% DR temperature-214 C.

EXAMPLE VI Percent by weight Polyvinyl acetal phenol-formaldehyde resin 99.74 Zinc (as zinc urea) 0.26 50% DF temperature-206 C.

EXAMPLE VII Percent by weight Polyvinyl acetal phenol-formaldehyde resin 99.08 Zinc (as zinc urea) 0.92 50% DF temperature-214 C.

EXAMPLE VIII Percent by weight Polyvinyl acetal phenol-formaldehyde resin 91.0 Zinc (as zinc urea) 0.5 Hexamethoxymethylmelamine 8.5 50% DF temperature-231 C.

EXAMPLE IX Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.1 Zinc (as zinc naphthenate) 0.5 Hexamethoxymethylmelamine 3.4

50% DF temperature-228 C.

The zinc naphthenate was employed in the form of a solution in petroleum spirits of which the zinc constituted about 8% by weight.

EXAMPLE X IPercent by Weight Polyvinyl acetal phenol-formaldehyde resin 99.5 Zinc (as zinc naphthenate) 0.5 50% DF temperature-222 C.

EXAMPLE XI Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.8 Calcium (as calcium naphthenate) 0.3 Hexamethoxymethylmelamine 2.9

50% DF temperature-212 C.

Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.2 Manganese (as manganese naphthenate) 0.4 Hexamethoxymethylmelamine 3.4

50% DF temperature-230 C.

The manganese naphthenate was employed in the form of a solution in petroleum spirits of which the manganese constituted about 6% by weight.

EXAMPLE XIII Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.1 Cobalt (as cobalt naphthenate) 0.5 Hexamethoxymethylmelamine 3.4

50% DF temperature-220 C.

The cobalt naphthenate was employed in the form of a solution in petroleum spirits of which the cobalt constituted about 6% by weight.

EXAMPLE XIV Percent by weight Polyvinyl acetal phenol-formaldehyde resin 96.7 Iron (as iron naphthenate) 0.4 Hexamethoxymethylmelamine 2.9

50% DF temperature-232 C.

The zirconium octoate was in a petroleum spirits solution containing about 6% by weight zirconium.

A typical apparatus and process which may be employed in applying the insulating composition on wire and heat hardening it thereon is shown, for example, in Patent 2,994,624. While the compositions of the invention are particularly adapted for use as wire coating material, they may be found quite satisfactory for various other electrical insulation uses, whether in the form of coatings, films, sheets, potting, encapsulation, cast solids, or other forms. The compositions of the invention may be applied to a variety of metals, such as copper, aluminum or other conductor materials, whether in the form of wires, plates or other shapes, or may be used for coating insulating base materials for various purposes.

While for purposes of obtaining optimum properties in wire coatings it is preferable to include the hexamethoxymethylmelamine in the enamel mixture, this additive may be omitted while still obtaining desirable results in both wire coating and other applications.

Various other materials may be added to the described compositions, such as iillers, plasticizers, coloring agents, etc., without going beyond the scope of the invention.

In comparative tests made to demonstrate the improvement afforded by the present invention, a number of enamel coated wire examples were subjected to elevated temperatures while immersed in transformer oil and the dissipation factor of the enamel on the samples was measured at different temperatures. The wire samples were of .0508 inch diameter and were provided with 8 coats of the enamel composition having a total thickness of 4 mils.

The compositions of the respective wire enamels were as follows:

Sample A-phenol-formaldehyde polyvinyl acetal resin Sample B-phenol-formaldehyde polyvinyl acetal resin -i-zinc urea (Example V composition) Sample C-phenol-formaldehyde polyvinyl acetal resin -l-zinc urea+hexamethoxymethylmelamine (Example 1V) Sample D-phenol-formaldehyde polyvinyl acetal resin -l-lead naphthenate4-hexamethoxymethylmelamine (Example III) Sample E-phenol-formaldehyde polyvinyl acetal resin -l-zinc) octoate+hexamethoxymethylmelamine (Example II FIGURE 2 in the drawing graphically shows the results of the above tests. In the graph, in which dissipation factor in percent is plotted against the temperature, the curves represent the various enameled wire samples and are designated to correspond with the respective enamel compositions A-E, inclusive, described above. As will be seen, all of the insulating compositions B-E, inclusive, which contained additives in accordance with the invention, reached 50% dissipation factor at substantially higher temperatures than the unmodified wire enamel represented by prior art composition A. Composition B with a DF surge temperature of 214 C. thus exhibited an improvement of about 23 C. over composition A, while composition E showed an improvement of about 40 C. over Composition A.

The improvements thus afforded by the wire coating enamel of the invention in terms of better electrical properties at elevated temperature are obtained without sacrifice in the excellent solvent and abrasion resistant properties which have characterized the phenolic-modified polyvinyl acetal resin material lused in the past.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as corne within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A composition of matter consisting essentially of a heat-hardenable mixture of (l) a polyvinyl acetal phenolaldehyde resin and (2) a metal organic compound selected from the group consisting of zinc urea, lead naphthenate, zinc naphthenate, zinc octoate, manganese naphthenate, cobalt naphthenate, iron naphthenate, and calcium naphthenate.

2. An electrical insulating material consisting essentially of the heat-treated product of a mixture of (1) about 97.5 to about 99% by weight of polyvinyl acetal phenolaldehyde resin and (2) about .25 to about 2.5% by Weight of a metal in a metal-organic compound selected from the group consisting of zinc urea, lead naphthenate, zinc naphthenate, zinc octoate, manganese naphthenate, cobalt naphthenate, iron naphthenate, and calcium naphthenate, the stated proportions being based on total solids content of the mixture.

3. An electrical insulating material consisting essentially of the heat-treated product of a mixture of (1) about 87.5 to about 99% by weight of polyvinyl acetal phenol-aldehyde resin, (2) about .25 to about 2.5% by Weight of a metal in a metal-organic compound selected from the group consisting of zinc urea, lead naphthenate, zinc naphthenate, zinc octoate, manganese naphthenate, cobalt naphthenate, iron naphthenate, and calcium naphthenate, and (3) about 1 to about 10% by weight of hexamethoxymethylmelamine, the stated proportions being based on total solids content of the mixture.

4. A wire enamel comprising the heat-treated product of a mixture of (l) about 96.6% polyvinyl acetal phenolformaldehyde resin, (2) about 0.4% zinc in zinc octoate, and (3) about 3.0% hexamethoxymethylmelamine, the stated proportions being based on total solids content of the mixture.

5. An insulated conductor comprising a wire having thereon an insulating coating consisting essentially of the 7 heat-treated product of a mixture of 1) a polyvinyl acetal phenol-aldehyde resin and (2) a metal-organic compound selected from the group consisting of zinc urea, lead naphthenate, zinc, naphthenate, zinc octoate, manganese naphthenate, cobalt naphthenate, iron naphthenate, and calcium naphthenate.

6. An insulated conductor comprising a wire having thereon an insulation coating consisting essentially of the heat-treated product of a mixture of (l) a polyvinyl acetal phenol-aldehyde resin, (2) a metal-organic compound selected from the group consisting of zinc urea, lead naphthenate, zinc naphthenate, zinc octoate, manganese naphthenate, cobalt naphthenate, iron naphthenate, and calcium naphthenate, and (3) hexamethoxymethylmelamine.

7. An insulated conductor comprising a wire having thereon an insulation coating consisting essentially of the heat-treated product of a mixture of (l) about 97.5 to about 99% by weight of a polyvinyl acetal phenol-aldehyde resin and (2) about .25 to about 2.5% by weight of a metal in a metal-organic compound selected from the group consisting of zinc urea, lead naphthenate, zinc naphthenate, zinc octoate, manganese naphthenate, cobalt naphthenate, iron naphthenate, and calciun naphthenate, the stated proportions being based on the total solids content of the mixture.

8 An insulated conductor comprising a Wire having thereon an insulation coating consisting essentially of the heat-treated product of a mixture of (1) about 87.5 to about 99% by weight of a polyvinyl acetal phenol-aldehyde resin, (2) about .25 to about 2.5 by weight of a metal in a metal-oragnic compound selected from the group consisting of zinc urea, lead naphthenate, zinc naphthenate, zince octoate, manganese naphthenate, cobalt naphthcnate, iron naphthenate, and calcium naphthenate and (3) about l to about l0 %by weight of hexamethoxymethylrnelamine, the stated proportions being based on the total solids content of the mixture.

References Cited UNITED STATES PATENTS 2,730,466 l/1956 Daszewski 117--232 2,283,353 5/1942 Clare 260-19 3,072,596 1/1963 Lavn et al. 260-844 3,313,651 4/ 1967 Burns 260-839 DONALD E. CZAIA, Primary Examiner.

W. E. PARKER, Assistant Examiner.

U.S. Cl. X.R.

ll7-l28.4, 132; 161-215; l74-ll0; 1260-839, 844

gyg@ UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIDN Patent No. 3, #124, 8324 Dated May 6, 1969 Inventor(s) Ralph G. FlOWeIS et al It is certified that error appears'in the above-identified pat-ent and that said Letters Patent are hereby corrected as show-n below:

Column l, line TO, before "addition" enhanced in electrical and mechanical properties by the 6, line 75; 1insulating;" should be insulation 7, line 4, the second comma should be deleted 8,V line 6, "organic" is misspelled SIGNED AND SEALED MAH 1 01970 (SEAL) um Edmnnmh" 1"- y mmm: n saaum .m Amming Offir Oonmiasioner of Patota. 

